Introduction to Wireless Communications Flashcards

This flashcard set covers the fundamental concepts of wireless communications, including electromagnetic wave properties, frequency bands, cellular evolution, IoT technologies, and technical challenges like multi-path fading and noise-limited systems.

Electromagnetic waves

Electric and magnetic field variations occurring in space and other propagation media where vibrations at a point excite neighbor vibrations, causing the wave to travel.

Free space

Technically defined as a vacuum, but in wireless radio, it may imply propagation media like the Earth's atmosphere that allow electromagnetic waves to travel.

VLF (Very low frequency)

A frequency band from $3\,kHz$ to $30\,kHz$ with wavelengths from $100\,km$ to $10\,km$, primarily used for navigation.

UHF (Ultra high frequency)

A frequency band from $300\,MHz$ to $3\,GHz$ with wavelengths from $1\,m$ to $10\,cm$, used for television, satellite communication, cellular telephones, and radar.

EHF (Extremely high frequency)

A frequency band from $30\,GHz$ to $300\,GHz$ with wavelengths from $1\,cm$ to $1\,mm$, used for radar and satellite communication.

1G

The first generation of cellular networks in the 1980s using analog phones and standards like NMT, AMPS, and TACS.

5G NR

The cellular generation of the 2020s characterized by eMBB (enhanced Mobile Broadband), URLLC (Ultra-Reliable Low Latency Communications), and mMTC (massive Machine Type Communications).

User Equipment (UE)

The mobile device or terminal used by a subscriber to connect to the Radio Access Network (RAN) in a wireless telecommunications system.

Core Network (CN)

The central part of a telecommunications network that provides various services to customers who are connected by the access network.

MEO (Medium Earth Orbit) Satellites

Satellites orbiting at a medium altitude, examples of which include the GPS, GLONASS, Galileo, and COMPASS navigation systems.

Wi-Fi 7 (802.11be)

A WLAN standard expected in 2024 providing a theoretical maximum data rate of $46\,Gbps$ across $2.4\,GHz$, $5\,GHz$, and $6\,GHz$ frequencies.

Zigbee

A low-power, low-data-rate WPAN technology based on IEEE 802.15.4 that uses sub-GHz and $2.4\,GHz$ frequencies.

LoRaWAN

A technology using LoRa spread-spectrum modulation for long-distance IoT networks in a star-of-stars topology, typically for smart cities or industrial applications.

ISM bands

Frequency bands available to the general public for Industrial, Scientific, and Medical purposes, such as the $2.4\,GHz$ band.

Broadcast effect

The ability of an access point to supply information to many receivers simultaneously; however, it leads to interference and the hidden terminal problem.

Hidden terminal problem

An issue in wireless networks where nodes that are physically apart cannot sense each other's transmissions, potentially leading to collisions.

Multi-path propagation

A phenomenon where signals arrive at the receiver from different paths due to obstacles, resulting in variations in amplitude, delay, and angle.

Inter-Symbol Interference (ISI)

An impairment caused by multi-path effects where a signal arrives through different paths with different delays, causing bits to overlap.

Boltzmann’s constant ($k_B$)

A physical constant used in calculating thermal noise power, valued at $1.38 \times 10^{-23}\,J/K$.

Noise Factor ($F$)

The ratio of the input Signal-to-Noise Ratio to the output Signal-to-Noise Ratio ($SNR_{in} / SNR_{out}$).

Free Space Loss (FSL)

A parameter assuming ideal atmospheric conditions where no EM energy is lost to dissipation, but power density decreases as the wave spreads out.

Path loss exponent ($\alpha$)

A unitless value that describes the rate at which path loss increases; it ranges from $2$ for free space to $8$ for obstructed building propagation.

Breakpoint distance ($d_{break}$)

The distance at which ground-reflected waves become nearly $180$ degrees out of phase with the direct path, causing severe signal cancellation.

Fade Margin (FM)

An attenuation allowance or 'fudge factor' added to the link budget to account for non-ideal propagation characteristics like multi-path fading.

Link Budget

An accounting of all gains and losses in an end-to-end system used to determine the transmit power necessary for a receiver to meet its sensitivity threshold.

Receiver Sensitivity ($P_S$)

The minimum received power level required for the receiver to process the signal accurately.